This invention relates to a corrosion monitoring system for testing the corrosive effects of certain fluids by simulating the high temperature, high pressure, and flow conditions experienced in the production tubulars of oil and gas wells. Various materials may be tested to determine their corrosion-resistant properties under controlled conditions and to determine the effects of various corrosion inhibitors.
In the production and handling of oil and gas, the tubulars and vessels which transport and store the petroleum products are often subject to highly corrosive fluid steams. Particularly severe corrosion may occur where the production contains high concentrations of carbon dioxide or hydrogen sulfide. Since corrosion rates may vary greatly as the temperatures, pressures, and flow conditions vary, it is important to test for corrosion under actual flow conditions. This may become difficult when the actual conditions are extreme, i.e., high temperatures, high pressures, and high velocity flow, and where the locations to be tested are inaccessible. For instance, in deep sour gas wells, actual well conditions may reach bottom hole pressures up to 20,000 psi and temperatures of 450.degree. F., and depths at which the most severe corrosion may occur may be greater than 20,000 feet. In producing from these deep wells, the pressure-temperature conditions within the production tubing will decrease with decreasing depth according to the rate of production and cooling effects. Therefore, it is important in testing for corrosion to simulate the variable conditions which may exist along the length of the production tubing, while at the same time having the materials being tested readily available for inspection and analysis.
Because of the complex nature of the corrosion mechanism, corrosion rates may be best be determined by exposing the corrodable material to be tested to a corrosive environment in and out of the presence of corrosion inhibitor candidates. The most common techniques have been to rely on the weight loss after corrosion of a specimen of the material being tested. However, at inaccessible locations, these techniques have the disadvantage that the corrodable material may not be readily or economically retrieved for the weight loss determination. Other types of corrosion monitoring techniques have been developed to remedy this situation. Radioactive tracers have been developed so that corrosion determination may be accomplished at a position remote from the location of corrosion without recovering the test specimen which has been placed downhole. Some of these tracer techniques would only indicate the point at which a preselected degree of corrosion had taken place. However, these techniques have the earlier mentioned disadvantage that the tracer units had to be replenished periodically, resulting in time consuming and expensive operations where the location of corrosion determination was not readily accessible. Other tracer techniques, such as the radioactive sleeve technique described in U.S. Pat. No. 3,348,052 issued to Raifsnider et al have attempted to incorporate a minor amount of radioactive material in a specimen which gives a resulting composition having similar corrosion characteristics as the material being monitored. However, it was found that results were sometimes inaccurate due to uncertain calibration factors in calculating corrosion rates from the radioactive sleeves.